A CHALLENGE FOR LOCAL AUTHORITIES AND INDUSTRY

To take account of climate change and the twin needs of economic and demographic growth which increase demand for water, desali-nation offers an effective and secure supply for regions affected by water scarcity.The gap between the available water resource and our municipal and industrial needs will reach 40% by 2030, and the number of people living in regions affected by severe hydric stress is expected to increase by a billion to 3.9 billion. The most severely affected re-gions will be North Africa, the Middle East, Northern China, Southern India, Pakistan and certain parts of the United States and Mexico.At the same time, 39% of the world’s population live less than 100 km from the sea and 60% of the world’s biggest cities in coastal areas do not have access to freshwater.

INSTALLED CAPACITY EXPANDING FAST

Desalination was first developed in the Arabian Peninsula, then adopted for islands, especially in the Mediterranean (Cyprus, Malta and the Spanish Islands), and then extended to other countries with a shortage of freshwater (Cape Verde, Mexico, California, Florida, Israel, etc.)Nearly 200 million people worldwide are now served by desalinated water from around 17,000 installed plants. In 2013, around 74 million m3 will be produced per day. Installed desalination capacity is expec-ted to double by 2016 to reach around 125 million m3 per day, with the biggest increase in capacity in the Middle East.

DESALINATION TECHNOLOGIES

Two main technologies are used for desalination on an industrial scale to produce freshwater from seawater or brackish water: dis-tillation (heat treatment) and reverse osmosis (membrane process).

Distillation

Distillation is the oldest technology used to obtain salt-free water from seawater or brackish water. It uses a heat source to evaporate

the water into steam and a cooling source to condense the steam into desalinated water. Regardless of the salt levels in the water to be treated, the water produced will generally have a final salinity below 10 mg/L.Distillation requires a substantial amount of heat energy and has to be coupled with other heat-producing applications (hot water or steam, a power source, etc.), which must be located nearby.To improve the water-produced/steam-deployed ratio, and there-fore lower the cost of freshwater production, distillation can have multiple effects: the heat produced by the condensation of steam in the first stage is reinjected into the bundle of boiler tubes of a second evaporator. Increasing the number of effects adds to the boi-ler requirements.

Distillation has mainly been developed in oil and gas producing countries, where it can be linked to thermal power facilities and thus use the heat they emit to produce evaporation. The advantage of this technique is that it does not require special pre-treatment of the water before its evaporation.

Reverse osmosis

The phenomena of osmosis and reverse osmosis have been known about for approximately one hundred years. But it was not until the 1960s, with the development of synthetic mem-branes, that these principles became an industrial reality. Since the first reverse osmosis membranes in cellulose acetate, a large number of organic membranes (made of polymers) and even mineral membranes have gradually been added to the list.A reverse osmosis membrane only allows water to pass through and it retains all the solutes, except for a few organic molecules very simi-lar to water (of low molecular weight and high polarity, e.g. ethanol, methanol, formol, etc.). These membranes are called permselective.How it works: when a concentrated saline solution is separated from a diluted solution by such a membrane, the difference in che-mical potential tends to push the water from the low-potential com-partment towards the high-potential compartment to dilute it, this is the phenomenon of direct osmosis.

Degrémont has a tradition of sharing its employees’ passion for water treatment with the public.To supplement the Water Treatment

Handbooks, Degrémont has issued the «Handbook Factsheets» to promote a better

understanding of the different techniques available and discovery of the new products and major technological changes.

Degrémont Water Treatment Handbook Factsheets

DESALINATION, the sustainable alternative

Desalination

Forecast of additional capacity - 2008-2016 (millions m3/d)

At the equilibrium point, the difference in pressure thus created is called osmotic pressure of the system. To prevent the flow of water across the membrane, pressure equal to the osmotic pressure has to be exerted on the “saline” fluid. To “reverse” the direction of the water flow, the pressure has to be higher than the osmotic pressure. This is the principle of desalination by reverse osmosis.

A reverse osmosis membrane does not have any pores. The wa-ter moves by flowing through the polymer structure which is always hydrophilic and “swelled” by the water.The reverse osmosis membranes are arranged in spiral wound mo-dules:

A flexible porous sheet (collector) (11) is placed between two flat membranes (10). This “sandwich” is sealed on three sides (12). The open side is welded to a cylindrical collector tube (3) on both sides of a perforated generator (8). Several assemblies of this type are separated from each other by a spacer (a flexible plastic grill) (9). The water to be treated (4) circulates in the spacer in parallel to the collector tube. The collector enables the permeate (5), i.e. the desali-nated water, to drain towards the axial collector (3).

The simplest reverse osmosis system consists of the following three elements:- a high-pressure pump to supply energy to the system;- a module or a set of modules containing the reverse osmosis mem-branes;- a valve on the discharge to maintain pressure in the system.If the proposed use of the desalinated water requires high quality (production of drinking water or industrial water from seawater, or ultrapure water), a two-pass system is deployed: some or all of the water produced by the first stage is pumped into a second stage which may be equipped with a different type of membrane. The dis-charge from the second pass is generally of better quality than the

supply to the first and can there-fore be recycled upstream from the first stage.

• Pre-treatment: in order to obtain water that is free of colloids, the water to be desalinated needs optimum clarification. Colloids are the cause of clogging (progressive deposit causing flow loss by obstruc-ting the free spaces in the spacers).

Well-designed pre-treatment is always the key to a reliable facility, involving a minimum of membrane washes and giving the reverse osmosis modules a longer life. It is also the most critical point which requires all the experience of the best professionals (knowledge of the water qualities encountered, knowledge of available technolo-gies, know-how in the design of a complete process that may com-bine decanting, flotation, simple filtration, membrane filtration, etc…)

• Washing: however much care is given to pre-treatment and good design of the installation, it is vital to provide for periodic washing of the modules. Washing can take a long time and can be difficult if hea-vy clogging of the channels in the separator grills has been allowed to build up, as this prevents the washing-products from reaching the core of the deposit. If washing is inadequate, it generally has to be repeated quickly, since the deposits left on the membrane attract crystallisation or biological recolonisation or constitute an obstacle to proper rinsing of the membrane.

• Remineralisation of the desalinated water may be necessary depending on the end use of the treated water.

ENERGY AND REVERSE OSMOSIS

The specific energy required for the reverse osmosis process has three functions: perform the pre-treatment; overcome the osmotic pressure at the membrane level; and overcome the membrane’s resistance to the flow of the water.The energy consumed by the reverse osmosis process is usually electrical and can come from a wide range of energy sources (e.g. wind, solar, etc.). Provided there is an electricity network available, reverse osmosis desalination plants can therefore be sited near raw water sources and water consumers.

Expenditure on energy ac-counts for over 50% of the operating costs and 20% of the price of the treated water. Over 60% of the energy is used during the first pass of reverse osmosis.

REASONS FOR THE DEVELOPMENT OF REVERSE OSMOSIS

Desalination by reverse osmosis is now the technique of choice for saline water desalination. After the first industrial realisation in the late 1960s and early 1970s, reverse osmosis took some time to become a mature technology for two reasons: its cost and energy consumption. Several avenues were explored to improve these points:• improvement in the characteristics of the reverse osmosis mem-branes, in terms of permeability, salt discharge, mechanical resis-tance and length of life;• deployment of energy recovery systems (such as turbine-efficiency of 80% - or pressure exchanger transfer-efficiency of 94% to 97%) and continuous improvement of the yield;• mastery of construction materials with the development of stainless steel having a better resistance to corrosion;• improvement in pre-treatment processes, enabling the scope of application of reverse osmosis membranes to be developed;• improvement in the discharge of salts and the permeability of the reverse osmosis membranes, which has improved the conversion rate from 30% to 45-60%, reducing the size of the pre-treatment faci-lities accordingly, and significantly contributing to the diminishing of the capital costs;•the use of speed controllers for pumps, reducing consumption peaks at start-up and adapting the speed to the pumps’ operating conditions;•linking the plant to a wind farm to avoid increasing greenhouse gas emissions or dependence on fossil or fissile fuels.

Degrémont Water Treatment Handbook Factsheets

Degrémont Water Treatment Handbook Factsheets

DEGRÉMONT OFFERS DEDICATED DESALINATION SOLUTIONS AND TECHNOLOGIES to safeguard populations affected by water shortage and serve industry

With its mastery of pre-treatment, reverse osmosis and reminera-lisation processes, and its Build–Operate expertise, Degrémont de-velops innovative desalination technologies to optimise processes, reduce operating costs and lessen environmental impact. It offers a broad range of products and services to provide relevant technical and economic solutions for local authorities and industry.

SOLUTIONS COMBINING EXPERTISE AND INNOVATION

SeadafTM

This compact solution for cla-rification by rapid dissolved air flotation of saline water replaces the first filtration stage. It is use-ful for water that may present

occasional peaks of suspended solids and algal bloom.

SeacleanTM

This dual media (anthracite + sand) filtration technology is ideal for desalination plants of all sizes. It improves the performance of re-verse osmosis membranes, increases their lifespan, reduces washing equipment and cuts water loss.

UltramarineTM SmartrackTM

This metallic chassis can ac-commodate different types of ultrafiltration membrane modules. The system is stan-dardised and industrialised, reducing the time taken for implementation and al-

lowing to master the cost of membranes renewal.

SeaproTM 50K

This Degrémont range of standard reverse osmosis desalination plant elements has been developed based on feedback from its rea-lisations. Its advantages are: reduced construction time for a rapid complete build (15 months), limitation of technical and construction risks, and general optimisation of costs (civil engineering, construc-tion, equipment, assembly, etc.). The most recent plant of this type is the SeaproTM 50K, which produces 50,000 m3/day, comprising:• water intake;• pre-treatment by SeadafTM rapid flotation, and ultrafiltration;• a reverse osmosis pass;• a remineralisation stage.

This plant is flexible in its design according to local conditions and each customer’s specific requirements.

OIL&GAS OFFSHORE

With its expertise in desalination and engineering know-how specific to offs-hore oil exploration and production, Degrémont designs and supplies units for desalination and sulphates removal to equip FPSO vessels.

OMOBILE / MobilePro

These mobile (truck-mounted) desali-nation units guarantee the quality and quantity of water required without capital outlay, anywhere in the world and for all types of industry. The trucks are rented and are equi-ped with reverse osmosis and ion

exchange units to produce industrial water. They guarantee the continuity of industrial water production in emergencies as well as anticipating purified water requirements during planned procedures.

Desalination robustness *

This modelling tool, developed jointly with Laborelec and GDF SUEZ, offers three advantages:• identification, by geographic region worldwide, of six typical seawa-ter compositions and their annual profile;• determination, according to profile, of the optimal dosages of chemicals to most effectively foresee the quality of the pre-treated water, thereby optimising the robustness of a desalination plant and its operating costs;• the choice of the best line of pre-treatment to optimise investment and operating costs.The tool is based on a statistical method using a database containing over 10 years of data (from pilot trials and plants).

Control build

This tool simulates the operation of a virtual desalination plant, ena-bling automated systems to be tested and parameterised upstream before being validated at the plant. It facilitates operational start-up on delivery of the plant and reduces the time needed for the com-missioning phase (two month reduction at the 450,000 m3/day Mel-bourne-Australia plant). The tool can also be used during the opera-tional phase to simulate optimisation methods and thus continually improve performance.

* The robustness of reverse osmosis plants is defined as the capacity to provide an appropriate flow and quality of drinking water, in accordance with the capacities of the plant and the guarantees of the membrane supplier.

UltramarineTM SmartrackTM S and L

Degrémont Water Treatment Handbook Factsheets

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FLAGSHIP REALISATIONS

For local authorities

MELBOURNE, AustraliaOne of the biggest reverse osmosis desalination plants in operation. It can produce and supply 450,000 m3 (extendable to 600,000 m3) of drinking water to the city of Melbourne per day.A prize-winner at the Global Water

Awards 2013 for its technical prowess and environmental integra-tion, the Victorian Desalination Plant has become the new bench-mark for the desalination industry worldwide.

AL DUR, BahrainComprehensive and secure pre-treat-ment.Key of the reliability of this 218,000 m3/day plant, the pre-treatment was designed to manage the strong concentrations of organic

matter and high incidence of algae off the Persian Gulf waters.

BARCELONA, SpainInnovative treatment of brines.Brines are mixed with water to be trea-ted by the Baix Llobregat wastewater treatment plant. The whole is treated before their dispersal, more than 3 km distant from pumping and at a depth

of 50 metres. The plant can produce up to 220,000 m3 of desalinated water per day, making it the biggest desalination plant in Europe.

RIYADH, Saudi ArabiaModular units in containers.33 brackish water desalination plants* were installed in just five months, at 14 sites, to treat the 165,000 m3/day sup-plying drinking water to the population of Riyadh and the surrounding area.

* modules in containers with an individual capacity of 5,000 m3/day, each composed of five containers: two for pre-treatment on dual layer filters, two for treatment by reverse osmosis membranes and one for final treatment and supply pumps.

For industry

MINERA ESCONDIDA, ChileThe reverse osmosis seawater desalination plant at Minera Escondida (Chile’s second biggest copper producer/exporter) produces 45,000 m3/day of process water for its mine in the Antofagasta region at an altitude of 2,800 metres.

FPSO PETROBRAS, BrazilKeppels FELS, world leader in the de-sign of offshore platforms, has ordered two desalination units and two sul-phate removal units for two FPSO (floa-ting production storage and offloading) vessels for the exploration and pro-

duction of offshore oil off the Brazilian coast.These two vessels are due to be delivered to Petrobras, a Brazilian company engaged in the research, extraction, refining, transporta-tion and sale of oil, which produces an average of 2.6 million barrels of oil equivalent per day.

KONIAMBO NICKEL SAS, New CaledoniaThe desalination plant produces 129 m3/h of drinking water and 53 m3/h of demineralised process water for boilers and cooling circuits at the Koniambo Nickel SAS complex, an industrial site near Koné in New

Caledonia. Omobile units were ordered to provide the excess production needed during commissioning of the plant and power station.

CHENGDU, ChinaThe wastewater treatment plant at the Petrochina refinery in Chengdu has a complex tertiary treatment line with total capacity of 67,000 m3/day. The performance of this treatment has enabled a reverse osmosis stage to be

included on the main water line.Separately, a specific treatment line with capacity of 10,300 m3/day, also by reverse osmosis, is dedicated to the treatment of brines. The quality of the water treated allows the reuse of 23,300 m3/day for the plant’s processes.

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